In recent years, techniques in which a layer having high permittivity is formed on a composite printed-wiring board or the like, and this layer is used in a condenser or the like have been known. This layer having high permittivity is prepared by, for example, methods in which a fibrous reinforcement such as glass fibers is impregnated with an organic solvent solution comprising a thermosetting resin with inorganic powders of high permittivity added in the solution, in order to offset brittleness of the thermosetting resin, and the solvent is removed by baking to cure the resin, and so on. In the conventional methods, however, it has usually been difficult to obtain a layer having high permittivity such as 30 or greater or 50 or greater.
In addition, attempts have been made to obtain dielectric layers of high permittivity using various kinds of inorganic powders. For example, it is known that a dielectric layer of high permittivity could be obtained by addition of Fe3O4, ZnO+ carbon or the like as inorganic powders to polystyrene. However, this system has a disadvantage that even though the permittivity can be increased, the dielectric loss tangent of the resulting dielectric layer increases, and therefore the amount of heat generated in the dielectric layer in the alternating current electric field increases, which may cause degradation of the multilayer printed-wiring board with a dielectric film provided thereon and the like, and failures such as destruction of joints due to thermal stress, leading to situations in which reliability and endurance of the semiconductor board are likely compromised.
In addition, for example, a composite material of high permittivity containing metal-coated powders of high permittivity and non metal-coated powders of high permittivity is described in Japanese Patent Laid-Open No. 6-84407, but when a composite material with permittivity of 30 or greater is to be obtained, for example, by the method described in the aforementioned publication, the dielectric loss tangent is worsened, thus making it difficult to obtain a composite material having high permittivity and small dielectric loss tangent.
On the other hand, usually, the method is well known in which inorganic powders of high permittivity are baked at a high temperature to form a dielectric layer in order to obtain high permittivity. However, there is a disadvantage that this method cannot be applied in the case where the dielectric layer is formed in a situation in which electronic parts are mounted on the wiring board, and thus is incapable of being applied commonly to processes for producing various kinds of semiconductor boards, because baking at a temperature as high as, for example, 1000° C. is required (the problem described hitherto is referred to as “Disadvantage 1”).
Therefore, it has been desired that a dielectric layer of high permittivity with reduced heat loss is provided by low-temperature baking, and that inorganic particles and a composition capable of providing such a dielectric layer are produced (Problem 1).
In addition, screen printing and the like are known as methods of forming the dielectric layer, but they have a disadvantage that as the board is upsized and fineness of wiring is enhanced, requirement for accuracy of positions of patterns becomes so vigorous that it cannot be satisfied by usual printing (Disadvantage 2).
Therefore, for coping with Disadvantage 2 in addition to Disadvantage 1, it has been desired that a dielectric layer of high permittivity with reduced heat loss is provided by low-temperature baking, and that a dielectric-forming composition capable of forming patterns of higher dimensional accuracy is produced (Problem 2).
On the other hand, in recent years, low permittivity and low dielectric loss tangent have been required as properties of materials for package boards in association with increased frequencies of signals, and therefore the mainstream of materials for package boards has been changed from ceramics to resins. Under such a background, techniques relating to printed-wiring boards using resin substrates include, for example, a technique disclosed in Japanese Patent Publication No. 4-55555. In this publication, a method is proposed in which an interlayer resin insulation layer is formed on a glass epoxy board with an inner conductive circuit formed thereon using epoxy acrylate, and subsequently openings for formation of via holes are formed by photolithography method, its surface is subjected to roughness treatment, and a plating resist is provided thereon, then an outer conductive circuit and via holes are formed by plating treatment.
For the interlayer resin insulation layer composed of a resin such as epoxy acrylate, however, in order to ensure adhesion to the conductive circuit as a conductor, its surface and the surface of the conductive circuit must be roughened. Therefore, there is a disadvantage that when high frequency signals are transmitted, they are transmitted through only the roughened surface area of the conductive circuit due to the skin effect, and a noise occurs in the signal due to irregularities of the surface. This disadvantage has been significant especially when the resin substrate having lower permittivity and lower dielectric loss tangent compared to the ceramic board is used.
In addition, the resin substrate has a disadvantage such that it tends to accumulate heat because its heat radiation is poor compared to the conductive board and ceramic board, and consequently the diffusion rate of copper ions constituting the conductive circuit is increased, thereby setting up a migration to cause rupture of the interlayer insulation. Then, for solving the problems described above, the technique is proposed in Japanese Patent Laid-Open No.7-45948 and Japanese Patent Laid-Open No. 7-94865 in which a resin is coated and formed by spin coating or the like on one side of a board made of resin or the like, and a metal (chrome, nickel, titanium, etc.) capable of improving adhesion to the conductive patterns is provided on the resin layer.
However, in the situation in which it is strongly desired to further reduce the size of the printed-wiring board having the IC mounted thereon for downsizing the entire device such as a cellular phone equipped with the printed-wiring board, the area on which electronic parts such as a resister and condenser other than IC chips is reduced, thus making it increasingly difficult to implement those electronic parts on the printed-wiring board.
Therefore, it has been required that a multilayer circuit board having a condenser funcation in a buildup wiring layer (Problem 3) should be provided.
In addition, a wiring board provided thereon with a plurality of layers including a signal layer, a power layer, a grounding layer and the like via an electrical insulation layer is used in the semiconductor device. Recently, even the semiconductor device containing plastic moldings has come to deal with extremely high-speed signals, and therefore the electric properties of the semiconductor device dealing with such high-speed signals have become controversial. That is, in the semiconductor device, for example, fluctuations of signals in switching affect the power supply line to cause fluctuations in voltage of the power supply, and fluctuations on the power supply side affect the grounding side, and these actions become significant as the speed of the signal is increased.
In the case of a single-layer wiring board, it is known that for the power potential and the grounding potential when the signal goes into switching, the power potential is significantly fluctuated due to ON-OFF of the switching signal. As a method for curbing such fluctuations in voltage, it is known that a decoupling condenser for curbing fluctuations by increasing an electric capacitance between the power supply line and the grounding line at a position close to the semiconductor chip to absorb fluctuations in potential by the electric capacitance.
However, in connection with this conventional wiring board, it is possible to cope with a rise in speed of the signal transmitted and the growth of power noises associated with high-density mounting by enlarging the width of the signal layer and increasing the number of mounted bypass condensers in making a design of wirings, but coping with them in this way results in a problem in which high-density mounting of electronic circuit components on the wiring board cannot be achieved. Furthermore, wiring board of low permittivity such as fluorine resin substrates have come to be applied for enhancement of signal speed. For these wiring boards, however, the same material is applied to the power supply system as well, the bypass condenser had to be used to cope with the power noise. In addition, techniques in which the wiring board is coated with a material of high permittivity are disclosed in Japanese Patent Laid-Open No. 5-37161 and Japanese Patent Laid-Open No. 5-160334, but the techniques have a disadvantage that a sufficient condenser capacity cannot be obtained if the area of the wiring board is reduced (Problem 4).
The present invention is to solve such problems associated with the prior art, and has the following objects.
The present invention is to solve the problem associated with the prior art as described above (Problem 1), and aims to provide inorganic particles and a dielectric-forming composition capable of forming dielectric layers of high permittivity with reduced heat loss and capable of being baked at a low temperature, and a film of high permittivity formed of this composition, and an electronic part comprising this film of high permittivity (Invention 1).
Also, the present invention is to solve the problem associated with the prior art as described above (Problem 1), and aims to provide dielectric layers with conductive foils of high permittivity with reduced heat loss and capable of being baked at a low temperature. In addition, the invention aims to provide condensers comprising such dielectric layers with conductive foils (Invention 2).
In addition, the present invention is to solve the problem associated with the prior art as described above (Problem 2), and aims to provide a dielectric-forming composition capable of forming in good dimensional accuracy a dielectric layer of high permittivity with reduced heat loss and capable of being baked at a low temperature, a photosensitive transfer film, and a dielectric and an electronic part formed of this composition (Inventions 3, 4).
The present invention is to solve the problem associated with the prior art as described above (Problem 1), and has as its object provision of ultrafine particle-resin composite particles capable of forming a dielectric layer of high permittivity with reduced heat loss and capable of being fired at a low temperature, a dielectric-forming composition, a dielectric with conductive foils formed of this composition, and an electronic part comprising this dielectric (Invention 5).
The present invention has been made to solve the above described problem with the prior art (Problem 3), and aims to provide a multilayer circuit board having a condenser function in a buildup wiring layer, and to provide a method allowing this multilayer circuit board to be produced advantageously (Invention 6).
The present invention has been made to solve the above described problem with the prior art (Problem 4), and has as its object provision of a wiring board having at least a signal layer, a power layer, a grounding layer and an insulation layer, wherein the wiring board contains a condenser having a large capacitance with a dielectric layer provided between the above described power layer and grounding layer (Invention 7).